Similar to Zoodiacs, ABC stay alive although the numbers are poor. The Alphabet Union monsters were wiped out from the competitive scenes when the Zoodiacs arrived, despite dominating the metagame for the initial weeks of October 2016. The Forbidden & Limited List which arrived at the start of 2017 ended the struggle of ABC as a deck, as their problems added on in the form of their key card being limited - Union Hangar.

Now, with a little innovation and help from some new friends, ABC decks might have just what it takes to keep afloat, although it won't be as easy as before.

There are still plenty of reasons to pick ABC as a deck. Apart from some obvious non-competitive related factors such as being a Union fan or Kaiba fan, ABC-Dragon Buster does pack a nasty effect that no monster in the competitive scenes can replicate. Its 3000ATK also puts it a little higher than Master Peace, the True Dracoslaying King if the Field Spell isn't accounted for in the equation. This is actually quite likely since you can just get rid of the field spell once ABC-Dragon Buster is summoned. Don't bother with Master Peace, the True Dracoslaying King, 9 out of 10 times it is protected by Monster effect immunity.

And like the most fearsome foe - the Dracoslaying King - in the current metagame, ABC-Dragon Buster can gain immunity to card effects as well, although the path to achieve that is slightly more tideous.

Another advantage of picking ABC as a deck is the ease of summoning Decode Talker. Not only does this reduce your worry for Link Summoning become a forseeable issue for the deck, Decode Talker also comes with a useful negation-protection ability. It is relatively easy to summon it in an ABC deck and also net yourself a few profitable effects on the way - dismantling ABC-Dragon Buster into its alphabetical counterparts, you can send all three Union monsters into the graveyard for the Link Summon, while triggering their graveyard effects along the way.

The True Draco archetype come into the picture as a result of arming the Union monsters with enough firepower to combat the metagame. Once again, if you can't beat them, join them. The Spell is there for the draw power and tribute fodder, but adding a Field Spell theme to the deck helps by reducing the chances of Terraforming being a dead card. I agree with Revival of the True Draco being maximised at three.
Not only is Tribute Summoning during your opponent's turn with a destruction the most disruptive factor of True Draco (or any archetype for that matter, Monarchs could skyrocket because of Ehther the Heavenly Monarch), when all copies of your Master Peace, the True Dracoslaying King is tribute summoned and exhuasted, you can use it as a reviving 2950ATK and DEF monster shield.

Union monsters are considered equipped spells.
Can you tribute them for Master Peace? Answer: NOPE

Gadgets can also special summon other Gadget monsters from the deck when destroyed from the hand by Dragonic Diagram. This makes Rank4 plays and Link Summons easier to achieve.

An interesting thing to note is the use of Interupted Kaiju Slumber in the Side Deck, not as a useable spell, but as a searcher and discard fodder to fuel ABC-Dragon Buster's or Twin Twister's discard cost. Also, it can be destroyed by Dragonic Diagram.

Conclusion

Master Peace, the True Dracoslaying King is a nice boss monster to bring out in a fight and at the very least, provide a smokescreen to the true nature of your deck, maybe leading to your opponent siding the wrong cards, or it can just distract your opponent while you gather your ABC Union monsters in the right places.

Other ways to go about building this deck are also available. You can try a Brilliant Fusion-based combo starter, but is very dependant on drawing into it to start your plays. Another boring alternative is to just spam it with traps while you play your Gadgets and Union monsters. Lastly, That Grass Looks Greener is a joy for any deck liking a well stacked graveyard but like Brilliant Fusion is a deck largely dependant on an engine/card to get the deck going, and this problem is only made worse by the fact that Ash Blossom & Joyous Spring negates this play-starters with ease. Pontentially shutting down the entire deck, and all they did was just discard a Hand Trap. An OP one for that matter.

Kaiba is love, Kaiba is life. (Dark Side of Dimensions made me a Kaiba fan)
While you are at it, why not check out this giveaway on Ygoprodeck. The second grand prize is a massive Kaiba giveaway.